This invention relates to improvements of a liquid crystal projector.
A liquid crystal projector usually uses, for instance, a TN (twist nematic) transmission type liquid crystal display panel for displaying a television image thereon, while projecting the displayed image on an enlarged scale onto a screen.
In this liquid crystal projector, the liquid crystal display panel is usually illuminated on the back side by illumination light from a light source lamp to make the displayed image brighter. The displayed image is enlarged through a projecting lens system to project as an enlarged-scle image on the screen located forward of the display panel.
The TN type liquid crystal display panel usually has a visual field angle of 10.degree. to 20.degree.. Nevertheless, the liquid crystal display panel is usually disposed so that it is perpendicular to an optical axis connecting its center and the center of the screen. With this arrangement, the direction in which the displayed image on the liquid crystal display panel can be seen best, i.e., the direction deviating by the visual field angle noted above, is not perpendicular to the optical axis. Therefore, the image that is seen when the display surface of the liquid crystal display panel is seen in a direction deviating by the suitable visual field angle, is projected on the screen. The brightness and contrast of the projected image on the screen, therefore, are inferior to the case where the screen is positioned so that it deviates by the suitable visual angle of the display surface of the liquid crystal display panel.
In another aspect, in the prior art liquid crystal projector, the liquid crystal display panel is illuminated on the back side directly by light from a light source lamp. Therefore, the liquid crystal display panel is heated by the infrared component of the illumination light. In addition, the temperature of the interior of the case of the liquid crystal projector rises due to heat generated by the light source lamp. Therefore, the liquid crystal display panel is heated and this eventually results in a collapse of the molecular arrangement of the liquid crystal. In other words, the normal display of the liquid crystal display panel deteriorates when the projector is used over an excessively long period of time.